The Jan. 12 earthquake in Haiti was hard to miss, but in the aftermath of the tragedy, the American media may have ignored several earthquakes that followed.
Though experts say the actual number of earthquakes is not increasing, with every passing year the likelihood of a massive earthquake in the Pacific Northwest increases.
February saw four large quakes: a 6.9-magnitude quake in the China-Russia-North Korea border region, a 7.0 in the Ryukyu Islands of Japan and an 8.8 in Chile that was followed by a 6.9-magnitude aftershock of. This list does not include the thousands of smaller earthquakes that happen every week.
March has seen a few already as well. Chile, for a second time, Vanuatu and Indonesia have had significant earthquakes this month. What does it all mean? Not much, say experts.
According to the U.S. Geological Survey, large-magnitude earthquakes have actually decreased in recent decades. More earthquakes are known about since the ability to record earthquakes has increased in the last few decades.
Just because we know about the seismic events doesn’t mean they weren’t occurring all along. Also, more people are at risk for being in an earthquake as the population increases.
“We’re really concerned about the big one, a subduction zone [earthquake] that will break from Northern California up to British Columbia. What is the analogy? Chile. That was a subduction zone earthquake,” said Scott Burns, a geology professor at Portland State.
The story of the Cascadia subduction zone was first told in the 2005 book, The Orphan Tsunami, by Brian Atwater. In it, Atwater describes the work done in the United States and in Japan to unlock the story of an unexplained tsunami experienced by Japan in the year 1700.
Many people in the Northwest may not be aware of the region’s vulnerability. According to Burns, until 1993, Oregon had minimal earthquake building codes. He credits the work of PSU geology Professor Curt Peterson for the changes.
The 900-mile subduction zone is located 50 miles from the coast. It runs from Arcata, Calif. to Vancouver, British Columbia.
“We have three sources of earthquakes,” Burns said. “We have movement along the faults in North America where the North American plate is moving to the west. The largest quakes we get there are about magnitude 6.5. The Portland Hills Fault is one of those and it runs right behind PSU.”
Another source of earthquakes is the Juan de Fuca plate along the West Coast.
“The largest we get there is magnitude 7.3,” Burns said. “Where the two plates are locking, where the Juan de Fuca plate is going under North America, we get up to 9.0.”
“This is earthquake country and we need to be prepared,” he said.
Things people can do to be prepared at home include caching water safe for drinking, knowing where the natural gas turn-off device is in your home and strapping your water heater in so it doesn’t fall over.
Geology Professor Ken Cruikshank said that when he lived in California, he kept a pair of shoes and gloves next to his bed.
“If an earthquake happens in the middle of the night, many injuries are sustained from crawling through broken glass to get out of the house,” he said.
Cruikshank said that everything known about the Cascadia subduction zone is extrapolated from evidence in the geologic record.
“Anything we have is what we’ve gleaned from the historical records. Even with that orphan tsunami, we’re still assuming that it was [the North American plate] that produced the one that arrived in Japan. It’s likely but it was 300 years ago,” he said.
According to Cruikshank, the Chilean earthquake was expected because the convergence rate is much faster than the North American plate.
“They’re getting magnitude eights every couple of centuries,” he said.
Comparing that to North America, where the recurrence interval is averaged to be 500 years, Cruikshank said, “Let’s say [the earthquakes] are 500 years apart. Well, we haven’t even been through one cycle yet.”